Recently, products including solid-state light sources such as a light-emitting diode (LED) and a laser diode (LD) have been increasingly used. The solid-state light sources are adopted as light sources used in projectors for presentation and digital cinema, instead of mercury lamps, xenon lamps, and the like used in related art. The solid-state light sources such as LEDs have advantages such as having long lifetime, no replacement of lamps, which is necessary in related art, and lighting-up immediately after power-on.
Such a projector includes a type in which a solid-state light source such as an LED is directly used as a light source. On the other hand, there is another type in which a light emitter such as a phosphor, which is excited by excitation light to emit light, is used as a light source. In this case, the solid-state light source is used as an excitation light source that outputs excitation light.
For example, a light source device disclosed in Patent Literature 1 includes first and second solid-state light source groups, first and second reflecting sections, and a light collecting optical system. The first and second solid-state light source groups are arranged so as to have different optical-axis directions. The first reflecting section reflects light from the first solid-state light source group so as to follow a traveling direction of light from the second solid-state light source group. The second reflecting section reflects the light from the first and second solid-state light source groups, whose traveling directions are aligned with each other, such that the interval between the optical axes becomes short. The light collecting optical system is formed of a plano-convex lens having an aspheric surface and collects the light reflected by the second reflecting section to a predetermined light-collecting position (see paragraphs [0047] to [0056], FIG. 2, etc. of Patent Literature 1).